1. Field of the Invention
The present invention relates to a Group III nitride semiconductor light-emitting device exhibiting improved light extraction efficiency and the production method therefore.
2. Background Art
The Group III nitride semiconductor light-emitting device has been used as a light source for emitting white light, and particularly the demand for illumination or display backlight is increasing.
The Group III nitride semiconductor light-emitting device generally has a structure in which an ITO transparent electrode is formed on a p-contact layer to diffuse current. Patent Document 1 discloses that p-GaN/p-AlGaN may be used as the p-contact layer. However, there is no mention about the reason for forming a p-AlGaN layer.
Patent Documents 2 and 3 disclose a structure in which p-AlGaN/GaN/p+-AlGaN is repeatedly deposited on a p-contact layer of p-GaN. This is to improve the current diffusion efficiency in the main surface direction of the device by using two-dimensional electron gas generated at the interface between GaN and AlGaN.    Patent Document 1: Japanese Patent Application Laid-Open (kokai) No. 2008-47864    Patent Document 2: Japanese Patent Application Laid-Open (kokai) No. 2006-313888    Patent Document 3: Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2010-512017
A high output Group III nitride semiconductor light-emitting device is demanded in illumination applications. However, there is a problem that the Group III nitride semiconductor light-emitting device has poor light extraction efficiency. One of the causes for the deterioration of the light extraction efficiency is the reflection at the interface between the p-contact layer and the transparent electrode. When the p-contact layer comprises p-GaN, and the transparent electrode comprises ITO, the p-contact layer has a refractive index for blue light of about 2.3, and the transparent electrode has a refractive index for blue light of about 1.9, thus the refractive indices are quite different. Therefore, a part of the light emitted from the light-emitting layer cannot be extracted from the device because the light is totally reflected at the interface between the p-contact layer and the transparent electrode.
Patent Documents 1 to 3 do not describe a problem of the above reflection at the interface between the p-contact layer and the transparent electrode.